I recently changed the tires on my 2003 Maruti 800 MPFI 5-speed. The broken patchy roads of Pune, would regularly ding and dent the wheel rims.
The old radial tires were of type: Goodyear 145/70R12-69S.
Some research revealed that:
The first number: 145 is the tire’s section width in millimeters from sidewall to sidewall, under no load. The second number 70 is the aspect ratio. That is, the ratio of the section height (height of the tire sidewall), expressed as a percentage of the width. In this case, 70% of 145mm is 101.5mm - the section height. The third number 12 is the metal wheel rim diameter (in inches) that the tire is meant for. Why do they mix inches and millimeters? Beats me! Couldn’t they have kept the spec. all metric and simply called it a 145/70R305?
The last number 69 is a load capacity index. It refers to the load carrying capacity of the tire at maximum air pressure. A 69 rated tire is good for 325 kg load on each wheel.
The ’’S’’ means that the tire is good for speeds upto 112 mph [180 km/hr]
Anyway, the choices with me for new radials for the Maruti 800 were
145/70R12 (the original size), 155/70R12 and 145/80R12.
Tire width translates to the area of contact with the road, influencing rolling friction and therefore fuel economy. I thought of upgrading to bigger rubber, for better comfort, without compromising the section width. So I chose the 145/80R12.
Purchased a set of 5 MRF ZVTS 145/80R12-74S radials, from Guardex Tyres, Chembur, Mumbai. They are an MRF tyres & service outlet.
The five new tires set me back by a total of Rs. 7, 875/=
The 74 rated tires are good for 375 kg load on each wheel.
I also had the wheels dynamically balanced and the suspension geometry angles realigned.
Positives:
The car now drives like a dream. The ride quality, absorption of noise, vibration and harshness is decidedly superior.
The ground clearance has gone up by 1.45 cm.
And the overall gearing is now 5.7% taller, so there will be better fuel economy.
And importantly, the bigger wheels don’t interfere with the wheel-wells, neither while steering nor while bouncing over a speed-bump. An initial concern which turned out to be a non-issue.
Negatives:
The overall diameter has increased from 507.8 mm to 536.8 mm. This means that the
speedometer and odometer indicate readings 5.7% less than actual. When the speedo indicates 100 km/hr, the car is actually doing 105.7 km/hr.
The spare wheel is now slightly larger than the space available in the recess in the luggage compartment. A welded steel strip that holds the wheel down has to be bent to accommodate the new wheelsize.
I put this discussion here as Mouthshut doesn’t currently have a review category for automotive tires and accessories.
If a moderator thinks this description would be better elsewhere, kindly move it there!